Thread: Low Battery level and dual batteries

I have an MY10 D4 with original battery (September 2010) and Traxide SC80 with an Optima yellow top. The system has been trouble free apart from getting 'low battery' warnings occasionally. It is my wife's daily drive of low km's with quite a few times of no driving so I was not too concerned about this. To overcome this I bought a Ctek 10 amp smart charger and wired it up to the main battery via the connector that came with the charger. Every so often I would just plug in the Ctek and give it a boost overnight.
Over the weekend I went to start the car and the computer screens went in to shutdown mode stating low battery. I could not start the car. The SC80 was flashing signalling that it had disconnected from the cranking battery due to low voltage, as designed.
I plugged in the Ctek and gave it a charge overnight. The SC80 signaled that it had reconnected with the cranking battery. The Ctek was up to the second last stage, which I thought was fully charged. One stage before trickle maintenance charge.
I tried to start the car next day after 18 hours on charge. The car did the same as previous day with screens shutting down and warnings on low battery. After several more attempts the car started and has started like normal ever since.
I brought it to Battery World and they checked out the battery. The technician mentioned it was reading the second battery so I unplugged the SC80 connector so he was only getting readings from the cranking battery.
After doing a hydrometer check he said the battery was about half charged. One cell had lower charge than the rest. I mentioned that the Ctek had indicated that it was fully charged by the LEDs being at the end of the line on the second last light.
The technician suggested that because I had a calcium battery and an AGM battery that I needed to charge them separately and change the settings on the Ctek to suit the type of battery.
I have since disconnected the SC80 connector plug and charged the cranking battery separately every night this week and hydrometer checks on the low cell has not improved, being on the edge of the red almost to the yellow. (bought hydrometer from Battery World). I will take it back to the battery shop on the weekend as, to their credit, they did not try to persuade me to buy a new battery as he said I needed to try charging separately first.
I would appreciate comments on this requirement to charge the batteries separately. I know these systems are not always as simple as they first seem.
The no start situation happened in my carport so there was no need for a jump start. As my SC80 does not have the jump start abilities of Tim’s later versions I would have had to get my jumper leads out to jump from the second battery to the cranking battery if I was away from home. I have been thinking about this since and am considering getting a second wire from the second battery with the same plug as what plugs in to the SC80 controller and swapping them over for jump start capabilities. i.e. the existing cable goes from positive on cranking battery and is connected to the SC80 relay via an easily connectable/disconnectable plug. If I have a second short cable to the positive on the second battery and swap the connector over at times when I need to jump start the cranking battery it should connect both batteries at all voltages, bypassing the SC80 relay. Can anyone see downside to this?
My last question is why the car did not start after the initial 18hr charge as the battery had enough charge to do so. My understanding is that to accurately measure battery volts you need to have a small flow of power. Does the Land Rover battery management system need this flow before it registers that the battery is now charged sufficiently to allow computer screens/systems to stay on and the car to start? It went from shutting itself down to normal after several attempts to start the car.
Sorry if this is a bit long winded. I did extensive searching on this and there is a heap of good stuff on this forum but it did not answer my questions above.
Sean

FWIW,my D4 is also not used a lot as we have company cars.It will often sit for a while and then do a long run,or sometimes a few short runs.
I noticed the SC80 flashing often,just doing its job,and the cranking battery on around 11.7 to 12.0V.

I also have a recently purchased a Ctek smart charger,and i have a plug permanently wired to the cranking battery and charge it every second weekend or so.
The cranking battery has AGM written on it,as does the optima auxiliary,so i set the charger to AGM and leave it.
I find that after the charger has fully charged both batteries(as they are connected together with the SC80),the batteries seem to be better charged than the state of charge the car gives the battery even after a good hour run on the highway.